1. Field of the Invention
This invention relates to polyphenylene etherpolycondensate block copolymers and to their preparation from substituted phenols and polycondensable monomers.
2. Discussion of the Background
Polyphenylene ether-polycondensate block copolymers are known in principle. DE-OS 15 20 019 describes the preparation of block copolymers from (i) polyphenylene ethers that have phenolic hydroxyl groups at both ends and (ii) polycondensates, such as polyesters or polyamides.
Thus, for example, a polyphenylene ether-polyester block copolymer can be prepared by esterifying a difunctional polyphenylene ether and 1,6-hexanediol with adipoyl dichloride in dry pyridine. Drawbacks of this method are the low reactivity of the phenolic end groups, the use of acid chlorides, and the use of pyridine.
Molding compositions that contain polyphenylene ether-polyester block or graft copolymers of the general formula A--Z.sup.1 --B and processes for preparing them are described in EP-OS 0 248 263. Variable A in this formula is a polyphenylene ether block and variable B is a polyester block. Variable Z.sup.1 is a linking group that is derived from a number of difunctional or polyfunctional compounds such as trimellitic anhydride monochloride, terephthaloyl dichloride, maleic acid derivatives, hexamethylenediisocyanate, 1,4-bis(2-oxazolinyl)benzene, or glycidyl methacrylate.
The starting material in this case is a preformed, initially unfunctionalized polyphenylene ether, and the linking is accomplished by reaction at the phenolic end groups (for example esterification with acid chlorides), on the aromatic rings (electrophilic substitution with N-methylolacetamide and methanesulfonic acid, Example 2), or on the alkyl groups (radical attack with glycidyl methacrylate, Examples 5-9).
The drawbacks in this technology are:
(i) the low reactivity of the sterically hindered phenolic end group; the average grafting yield based on the polyphenylene ether is only about 30%;
(ii) the nonspecific nature of the reaction in the attack on the aromatic rings or alkyl groups; the number of linking groups Z.sup.1 introduced and the position of substitution cannot be determined in advance; and
(iii) the formation of a large proportion of homopolymer in the radical attack of polymerizable functional compounds, such as glycidyl methacrylate; these homopolymers then have to be separated in a laborious manner.
A special case of polyphenylene ether-polycondensate block copolymers is described in EP-OS 0 193 741. This polycondensate, preferably a polyester, has liquid crystalline character. Starting from preformed polyphenylene ethers, the linkage takes place on the phenolic end groups in this case also, for example by reaction with acid chlorides.
Polyphenylene ether-polyamide block copolymers are prepared by reacting the phenolic end groups of preformed, unfunctionalized polyphenylene ethers with difunctional or polyfunctional coupling reagents that act as promoters for the subsequent polymerization of added lactam (EP-OS 0 211 201; Polym. Bull. (1987) 17 423). The low reactivity of the phenolic end groups, which requires the use of a large excess of promoter or industrially uncommon reagents such as sodium hydride, is a drawback here also. Further, the products contain only 10 to 46 wt. % block copolymer. This method is also limited to block copolymers whose polyamide segments are derived from lactams.
Polyphenylene ether-polyester graft copolymers in which a polyphenylene ether main chain is grafted with polypivalolactone chains in statistical distribution are described in EP-OS 0 243 271. The process requires the metallation of the polyphenylene ether, dissolved in tetrahydrofuran, with organometallic compounds such as n-butyllithium with rigorous exclusion of atmospheric oxygen, moisture, and residual solvents that contain easily abstractable hydrogen, such as alcohols.
The polyphenylene ether-polycondensate block copolymers and graft copolymers known from the state of the art are therefore available only by a laborious synthesis that comprises three separate steps:
1. preparation of a conventional unfunctionalized polyphenylene ether;
2. functionalization;
3. polycondensation of suitable monomers in the presence of this functionalized polyphenylene ether.
Alternatively, the following path, likewise comprising three steps, can be taken (for example, see EP-OS 0 248 263):
1. preparation of a conventional unfunctionalized polyphenylene ether;
1*. its functionalization as the case requires;
2. preparation of a polyester;
2*. its functionalization as the case requires;
3. coupling of polyphenylene ether and polyester by reaction in solution or in the melt.
In the normal case a mixture is formed that contains large fractions of the corresponding homopolymers. Furthermore, the synthesis is frequently limited to a specific polycondensate.